Thermal print heads are known for dot matrix printing on a writing surface. Generally, writing is accomplished by means of an array of resistive elements disposed in one or more rows along the surface of the print head. These resistive elements are heated when power is applied across them, thereby marking thermally sensitive paper disposed across the print-head surface. Alphanumeric or other characters are formed by selective energization of the resistive elements of the array on the print-head surface for selected periods of time, while the writing surface or paper moves relative to the print head.
The speed with which such printing can be accomplished has generally been limited by the amount of time required to bring a resistive element to the appropriate temperature to mark the writing surface, and conversely the amount of time required for the resistive element to cool and cease marking the paper. It is preferred to maintain the temperature of the resistive elements at a point just below that necessary to mark the writing surface, thereby permitting more rapid heating of the resistive elements to the temperature required to print, and resultant improvement in printing efficiency.